A skier of mass 64 kg starts from rest at the top of an 18° slope, points her skis straight down the slope and lets gravity pull her down the slope. The slope is 65 m long. Her speed at the bottom is 15 m/s. (a) Assuming zero air resistance, what is the magnitude of the frictional force between her skis and the snow? (b) What is the coefficient of kinetic friction between her skies and the snow?